"Half-elves and half-orcs may select racial favored class options, archetypes, traits, and so on, as if they were a full member of both races (a half-elf can select elf and human rules elements, a half-orc can select human and orc rules elements)"

So I am assuming Humans can take Archetypes that are for Half-???

In this instance I am referring to the Psychic Archetype, Terror Weaver:

No both half elves and half orc have a racial trait that says they count as both races. This is the reason they can take things requiring you to be of either race, as well as those for their own race. Humans do not have this racial trait so cannot take anything but human choices.

Humans can that the human feat Racial Heritage that allows them to count as another race. A human could take Racial Heritage half orc and qualify for half orc choices.

"Elf Blood: Half-elves count as both elves and humans for any effect related to race."

And Half-Orcs have this racial trait:

Orc Blood wrote:

Orc Blood: Half-orcs count as both humans and orcs for any effect related to race.

Humans don't have anything like that naturally. However, there is a feat in the Advanced Race Guide called Racial Heritage.

Racial Heritage feat" wrote:

The blood of a non-human ancestor flows in your veins.

Prerequisites: Human.

Benefit: Choose another humanoid race. You count as both human and that race for any effects related to race. For example, if you choose dwarf, you are considered both a human and a dwarf for the purpose of taking traits, feats, how spells and magic items affect you, and so on.